The invention relates generally to an annular apparatus, including an antenna and a transponder, useful in a tire for the purpose of transmitting tire or wheel data and, more specifically, to the method of assembly thereof.
It is common to employ annular apparatus, including an antenna, for electronically transmitting tire or wheel identification or other data at radio frequency. The apparatus includes a radio-frequency transponder comprising an integrated circuit chip having data capacity at least sufficient to retain identification information for the tire or wheel. Other data, such as the inflation pressure of the tire or the temperature of the tire or wheel at the transponder location, can be transmitted by the transponder along with the identification data.
It is known in the art to employ an annular antenna to transmit, at radio frequencies, data from a transponder contained within the structure of a tire or tire and wheel assembly. The antenna and transponder may be incorporated into a tire during xe2x80x9cpre-curexe2x80x9d manufacture. In practice, however, it is very difficult to do this. Both radial ply and bias ply tires undergo a substantial diametric enlargement during the course of manufacture. Bias ply tires are expanded diametrically when inserted into a curing press, which typically has a bladder that forces the green tire into the toroidal shape of the mold enclosing it. Radial ply tires undergo diametric expansion during the tire building or shaping process and a further diametric expansion during the course of curing. Any annular antenna and the electronic circuitry associated therewith built into the tire must be able to maintain structural integrity and the mechanical connection between the antenna and transponder package during the diametric enlargement of the tire during its manufacture. Once assembled into the tire, any detected malfunction in the antenna, transponder, or antenna to transponder connection that cannot be repaired destroys the utility of the tire and may necessitate a scrapping of the tire. Hence, placement of an annular antenna-transponder assembly into a tire during its manufacture carries risk that subsequent failure or breakage of assembly components will necessitate the destruction of the otherwise suitable host tire.
Not only is the risk of damage to an annular antenna-transponder system present during its incorporation into a tire during manufacture, but damage to such systems are not uncommon from operation of the tire on a vehicle. Loop antennas in known tire pressure monitoring systems have heretofore been placed into the tire during the curing process either at the crown of the tire, the bead of the tire, or the sidewall. Antennas and transponders located in the crown are subjected to substantial compressive strain and at the sidewall a high strain amplitude. Such locations represent high load and deformation regions of the tire. Consequently, antenna, transponders, and the connections therebetween in such locations are prone to breakage and mechanical or electrical failure.
A need therefore exists for a method and apparatus for mounting a transponder module in a pneumatic tire in such a manner that the transponder may conveniently be inserted, removed, replaced and/or maintained, either during tire manufacture or after. Additionally, the annular apparatus and method of employing same would operate to optimally locate the transponder sensors within a tire cavity to facilitate accurate measurement.
A further need exists to provide method and apparatus for mounting a transponder and an antenna for the transponder within a pneumatic tire, and to provide for a highly reliable magnetic coupling between the transponder and the antenna.
Still a further need exists to provide a method for mounting a transponder module in a pneumatic tire at any point in the tire manufacturing process, with minimal impact on tire performance.
In addition, a need exists to provide a method for assembly annular apparatus including a coupled annular antenna and transponder in a cost effective and efficient manner.
The subject invention overcomes the deficiencies in known systems and methods for coupling an annular antenna to an electrical device such as a transponder. An annular antenna is coupled to a transponder either directly or indirectly. According to one embodiment of the invention, a toroidal body composed of material having high electro-magnetic permeability is coupled to a transponder device by a winding. The antenna loop is passed directly through the center opening in the toroid and magnetically couples directly with the toroid body without utilization of a winding or mechanical connection. Electrical coupling occurs between the loop and the toroid, and therefore into the winding to the transducer because the current induced in the loop antenna from the transceiver magnetic field creates a magnetic near the loop. Thus, the magnetic field is induced directly into the toroid body that closely surrounds the antenna loop wire(s). Such a coupling is hereinafter designated as Direct Magnetic Coupling (DMC). The DMC approach allows the antenna loop to pass through the transponder package without a mechanical connection and therefore eliminates the problems with making and maintaining a mechanical connection between the loop wire and the transponder package. The winding coupling the toroid to the transponder package may be varied to accommodate optimum impedance matching. Consequently, the DMC technique provides a high energy coupling with high resistance to breakage since a mechanical connection between the antenna loop and the transponder is avoided. Furthermore, the process of attaching the antenna loop to a transponder is simplified and remote coupling between wire bundles or cables and transponders is facilitated. Moreover, the magnetic coupling between an annular antenna and transponder using the DMC technique is maintained in a continuous 360 degree read and dead zones in the interrogation area are avoided.
Pursuant to an aspect of the invention, the antenna and the transponder are at least partially embedded into a non-conductive carrier strip to form a ring assembly to render the antenna and transponder package unitarily transportable. Such an assembly may be incorporated into a tire during the tire manufacturing process but preferably is attached to the tire by adhesives or other known methods in a post-manufacture attachment procedure. The carrier strip serves at least a fourfold purpose. First, the strip protects the integrity of the antenna wire and transponder encapsulated therein. Secondly, the strip creates a unitary assembly that may be conveniently transported, inventoried, and deployed to retrofit existing tires with a monitoring system or to replace defective components should the need arise. Thirdly, the strip maintains the antenna in an intended optimal position relative to the transponder toroidal body through which it extends. Finally, the carrier strip serves to maintain an optimal orientation of the transponder to the tire cavity.
According to a further aspect of the invention, a method is provided for associating a loop antenna with an electronic device such as a transponder and the location of the antenna-transponder assembly on a tire in a position that protects the assembly from strain induced by tire operation and electro-magnetic interference from the wheel rim. The method further comprises the steps of coupling the loop antenna to the electronic device either directly or indirectly as through a toroidal body such as a transformer. A further step includes at least partially encapsulating the antenna and the electronic device package in a non-conductive carrier strip material so as to render the antenna and the transponder package unitarily transportable and to fix the relative positions of the antenna and transponder into respective optimal orientations.
According to a further aspect of the invention, a method of assembling an annular antenna and transponder apparatus is provided comprising the steps: extruding and curing the antenna and rubber cover; cutting the antenna wire and rubber cover to length; stripping the wire ends; feeding one wire end through a transponder body of high electro-magnetic permeability so as to establish an electro-magnetic coupling between the antenna wire and the transponder through the toroidal body; splicing the ends of the wire together to form an endless loop; injecting rubber around the transponder tag and stripped antenna wire ends.
The advantages of the invention, which will be apparent to those skilled in the art, are achieved by preferred and alternative embodiments that are described in detail below and illustrated by the accompanying drawings.